1. Field of the Invention
This invention pertains to a process for the selective solvent extraction of symmetrical tetrachloropyridine (sym-tet) from a mixture containing an aprotic solvent, iodide ions and symmetrical tetrachloropyridine. Symmetrical tetrachloropyridine is an important commercial product which is used extensively in the preparation of insecticides.
2. Prior Art Description
Symmetrical tetrachloropyridine is prepared through a variety of processes. In a process as taught in Russian Pat. No. 539,034, an alkali dialkyl phosphite in N,N-dimethylformamide is added to 4-iodotetrachloropyridine, to form the desired symmetrical tetrachloropyridine. The reaction is carried out at temperatures from 140.degree. C. to 160.degree. C.
In U.S. Pat. No. 3,538,100, symmetrical tetrachloropyridine is prepared from the reaction of 2,6-dichloropyridine and chlorine in the presence of a catalyst. Pentachloropyridine is also produced as a contaminating by-product. Sym-tet precipitates out of the reaction system as crystals.
Another method for producing symmetrical tetrachloropyridine is by the reaction of pentachloropyridine with an oxidizable metal (e.g., Zn) in the presence of an acid (e.g., aqueous HCl). According to Dean et al. in U.S. Pat. No. 3,993,654, this reduction reaction is run in an aqueous medium at a temperature of 110.degree. C. Dean et al. teaches the use of a water immiscible solvent, such as, perchlorethylene, to extract sym-tet from an aqueous medium.
It is desirous to obtain extractant solvents that selectively extract sym-tet.